Burner and Feed Apparatus For Flash Smelter

ABSTRACT

A burner for a flash smelting furnace. The burner includes a distributor for receiving pulverous feed material from a plurality of feed pipes. The distributor has at least one curved deflector that directs the feed stream in an evenly distributed annulus into the sleeve of the burner.

This application claims the benefit of U.S. provisional application No.61/483,432 filed on May 6, 2011, and U.S. provisional application No.61/539,594 filed on Sep. 27, 2011.

TECHNICAL FIELD

The present subject matter relates to flash smelting furnaces, andparticularly to burners and feed apparatus for flash smelting furnaces.

BACKGROUND

Flash smelting is a pyrometallurgical process in which a finely groundfeed material is combusted with a reaction gas. A flash smelting furnacetypically includes an elevated reaction shaft at the top of which ispositioned a burner where pulverous feed material and reaction gas arebrought together. In the case of copper smelting, the feed material istypically ore concentrates containing both copper and iron sulfideminerals. The concentrates are usually mixed with a silica flux andcombusted with pre-heated air or oxygen-enriched air. Molten dropletsare formed in the reaction shaft and fall to the hearth, forming acopper-rich matte and an iron-rich slag layer. Much of the sulfur in theconcentrates combines with oxygen to produce sulfur dioxide which can beexhausted from the furnace as a gas and further treated to producesulfuric acid.

A conventional burner for a flash smelter includes an injector having awater-cooled sleeve and an internal central lance, a wind box, and acooling block that integrates with the roof of the furnace reactionshaft. The lower portion of the injection sleeve and the inner edge ofthe cooling block create an annular channel. The feed material isintroduced from above and descends through the injector sleeve into thereaction shaft. Oxygen enriched combustion air enters the wind box andis discharged to the reaction shaft through the annular channel.Deflection of the feed material into the combustion air is promoted by abell-shaped tip at the lower end of the central lance. In addition, thetip includes multiple perforation jets that direct compressed airoutwardly to disperse the feed material in an umbrella-shaped reactionzone. A contoured adjustment ring is mounted slidingly around the lowerportion of the injector sleeve within the annular channel. The velocityof the combustion air can be controlled to respond to different flowrates by raising and lowering the adjustment ring with control rods thatextend upwardly through the wind box to increase or reduce thecross-sectional flow area in the annular channel. Such a burner for aflash smelting furnace is disclosed in U.S. Pat. No. 6,238,457.

Known burners of this type are associated with disadvantages that canadversely affect their performance. These include failure to achievemaximal mixing of the feed material with the combustion gas to optimizeoxygen efficiency within the reactor. In addition, such burners havelimited range of velocity control to optimize the performance of theburner relative to the feed material. Known burners are also associatedwith uneven distribution of feed material through the injector sleeve,which can also adversely affect their performance.

For example, the control rods that raise and lower the adjustment ringcan interfere with the even flow of air through the wind box and impedeoptimal mixing and combustion. It is also difficult to provide watercooling for the adjustment ring, and the ring has a tendency to becomesticky or misaligned on the injector sleeve.

In addition, dispersion of feed material by compressed air is less thanoptimal because the discreet jets used on known lance tips fail toprovide a continuous air curtain.

Moreover, known burner designs fail to include means for monitoring howwell centered the injector is within the annular channel, or mechanismsfor effectively adjusting the injector without having to shut down thefurnace.

It is a goal of the inventors to provide an improved burner and burnerfeed apparatus for a flash smelting furnace that provides better mixing,more optimal oxygen efficiency, improved control, and ease ofmaintenance.

SUMMARY

The following summary is intended to introduce the reader to the moredetailed description that follows, and not to define or limit theclaimed subject matter.

According to one aspect, a burner is provided for a flash smeltingfurnace. The burner includes a burner block, a wind box, an injector,and an injector surrounding structure. The block integrates with theroof of the furnace, and has an opening therethrough to communicate withthe reaction shaft of the furnace. The wind box is mounted over theblock and supplies combustion gas to the reaction shaft through theblock opening. The injector has a sleeve for delivering pulverous feedmaterial to the furnace and a central lance within the sleeve to supplycompressed air for dispersing the pulverous feed material in thereaction shaft. The injector is mounted within the wind box so as toextend through the opening in the block, defining therewith an annularchannel through which combustion air from the wind box is supplied intothe reaction shaft. The injector surrounding structure extends from thewind box through the opening in the block. One of either the injectorsurrounding structure and the injector is movable relative to the otherby control means exterior of the wind box so as to adjust thecross-sectional area of the annular channel and thereby control thevelocity of the combustion air supplied into the reaction shaft.

In some examples the injector surrounding structure is a collar movableby control means exterior of the wind box so as to adjust thecross-sectional area of the annular channel and thereby control thevelocity of the combustion air supplied into the reaction shaft. Thecollar may comprise a plurality of curved fins which pivot to expand orcontract the annular channel. Alternatively, the collar may comprise atleast one band which can be raised toward or lowered away from anoutwardly flared section on the sleeve to increase or reduce the annularchannel.

In other examples, the lower portion of the sleeve is upwardly taperedand the injector surrounding structure has a generally correspondingdownward taper, and the injector can be raised and lowered by controlmeans exterior of the wind box so as to adjust the cross-sectional areaof the annular channel.

According to another aspect, a burner is provided for a flash smeltingfurnace. The burner includes a burner block, a wind box, an injector,and an injector surrounding structure. The block integrates with theroof of the furnace, and has an opening therethrough to communicate withthe reaction shaft of the furnace. The wind box is mounted over theblock and supplies combustion gas to the reaction shaft through theblock opening. The injector has a sleeve for delivering pulverous feedmaterial to the furnace and a central lance within the sleeve to supplycompressed air for dispersing the pulverous feed material in thereaction shaft. The injector is mounted within the wind box so as toextend through the opening in the block, defining therewith an annularchannel through which combustion air from the wind box is supplied intothe reaction shaft. The upper portion of the sleeve of the injector ismounted to the lower portion of the wind box with respective flangesseparated by a compression gasket and provided with leveling adjusters.

According to another aspect, a burner is provided for a flash smeltingfurnace. The burner includes a burner block, a wind box, an injector,and an injector surrounding structure. The block integrates with theroof of the furnace, and has an opening therethrough to communicate withthe reaction shaft of the furnace. The wind box is mounted over theblock and supplies combustion gas to the reaction shaft through theblock opening. The injector has a sleeve for delivering pulverous feedmaterial to the furnace and a central lance within the sleeve to supplycompressed air for dispersing the pulverous feed material in thereaction shaft. The central lance includes an annular slot at its tipfor creating a substantially continuous air curtain.

According to another aspect, a burner feed apparatus is provided for aflash smelting furnace. The burner feed apparatus includes a distributorhaving curved deflector plates that direct the feed stream in an evenlydistributed annulus into the burner sleeve.

BRIEF DESCRIPTION OF DRAWINGS

In order that the claimed subject matter may be more fully understood,reference will be made to the accompanying drawings, in which:

FIG. 1 is an isometric view of a burner assembly and feed apparatus fora flash smelting furnace according to one embodiment.

FIG. 2 is an enlarged isometric view of the burner assembly of FIG. 1.

FIG. 3 is a cross-sectional view of the burner assembly of FIG. 2 withthe combustion air channel most open.

FIG. 4 is a cross-sectional view of the burner assembly of FIG. 2 withthe combustion air channel most closed.

FIG. 5 is a more detailed cross-sectional view of the lower portion ofthe burner of FIG. 3.

FIG. 6 is a more detailed cross-sectional view of the lower portion ofthe burner of FIG. 4.

FIG. 7 is an isolated isometric view of a portion of the collar assemblythat opens and closes the combustion air channel in the burner of FIGS.3 and 5.

FIG. 8 is an isolated isometric view of a portion of the collar assemblythat opens and closes the combustion air channel in the burner of FIGS.4 and 6.

FIG. 9 is an isolated perspective view of a portion of the control ringand support frame for the collar assembly of FIGS. 7 and 8.

FIG. 10 is an isolated cross-sectional view of the injector of theburner of the previous figures.

FIG. 11 a is a more detailed cross-sectional view of the tip of theinjector.

FIG. 11 b is an exploded isometric view of the tip of the injector.

FIG. 11 c is a similar isometric view of the tip of the injector, withinternal structures shown in dotted lines.

FIG. 12 is a more detailed cross-sectional view of the upper portion ofthe injector.

FIG. 13 is a plan view of the upper portion of the injector.

FIG. 14 is an isolated isometric view of a splitter box of the feedapparatus.

FIG. 15 is an isolated isometric view of a manifold connector of thefeed apparatus.

FIG. 16 is an isolated isometric view of the feed pipes of the feedapparatus.

FIG. 17 is an isometric view of the distributor of the feed apparatus.

FIG. 18 is an isometric view from below of the upper portion of thedistributor of FIG. 17, revealing the interior thereof.

FIG. 19 is a perspective view of a burner assembly according to a secondembodiment.

FIG. 20 is a cross-sectional view of the burner assembly of FIG. 19 withthe combustion air channel most open.

FIG. 21 is a cross-sectional view of the burner assembly of FIG. 19 withthe combustion air channel most closed.

FIG. 22 is a cross-sectional view of a burner assembly according to athird embodiment with the combustion air channel most open.

FIG. 23 is a more detailed cross-sectional view of the lower portion ofthe burner of FIG. 22.

FIG. 24 is a more detailed cross-sectional view of the lower portion ofthe burner of FIG. 22 with the combustion air channel most closed.

FIG. 25 is a perspective view of a burner assembly according to a fourthembodiment.

FIG. 26 is a cross-sectional view of the lower portion of the injectorof the burner of FIG. 25.

FIG. 27 is a more detailed cross-sectional view of the connectionsurrounding the injector of the burner of FIG. 25.

FIG. 28 is a cross-sectional view of the feed distributor of the burnerof FIG. 25.

FIG. 29 a is a cross-sectional view of an inspection port of the burnerof FIG. 25, with both its internal guard and external cover in theirclosed positions.

FIG. 29 b is a cross-sectional view of the same inspection port with itsinternal guard in its open position and its external cover in its closedposition.

FIG. 29 c is a cross-sectional view of the same inspection port withboth its internal guard and external cover in their open positions.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, specific details are set out to provideexamples of the claimed subject matter. However, the embodimentsdescribed below are not intended to define or limit the claimed subjectmatter. It will be apparent to those skilled in the art that manyvariations of the specific embodiments may be possible within the scopeof the claimed subject matter.

As shown in FIGS. 1-4, a burner assembly 13 is positioned above thereaction shaft of a flash smelting furnace. The base of the burnerassembly 13 is provided by a block 14 which integrates into the roof ofthe reaction shaft of the furnace. A wind box 15 is mounted above theblock 14 and an injector 16 having a sleeve 17 and a central lance 18extends through the wind box 15 and through a nozzle opening 19 in theblock 14. Above the wind box 15 is the material feed equipment,comprising air slides 20, splitter boxes 21, manifold connectors 12,feed pipes 22, and a distributor 23 which communicates with the sleeve17 of the injector 16. The central lance 18 of the injector 16 extendsupwardly beyond the sleeve 17 through the top of the distributor 23 to alance head section 24.

As seen in FIGS. 3 and 4, the burner assembly 13 rests on the burnerblock 14 which provides the main seal between the reaction shaft of thefurnace and the burner assembly 13. The block 14 is water-cooled and hasmultiple ports for access to burner components. The injector sleeve 17extends into the upper portion of the reaction shaft of the furnace. Thecentral lance 18 has a tip 25 at its lower end which extends below thesleeve 17. The lower rim 26 of the sleeve 17 is inwardly chamfered andthe lance tip 25 has a frustoconical shape and together they direct thefeed material outwardly. The lance 18 carries compressed air which isdirected horizontally from the tip 25. The compressed air furtherdisperses the feed material in an umbrella pattern. The opening 19 ofthe block 14 and the sleeve 17 define an annular channel through whichthe combustion air passes from the wind box 15 to the reaction shaft.

The wind box 15 communicates with the reaction shaft through a variablecollar 28 within the annular channel 27. The collar 28 provides a nozzlefunction so that the velocity of the enriched air can be controlled toaccommodate different flow rates. As shown in FIGS. 5-9, the collar 28comprises sixteen curved fins which pivot to expand or contract aroundthe lower portion of the injector sleeve 17. Eight inner fins 29 aretapered and have outwardly extending control arms 30. Eight outer fins31 overlap with the eight inner fins 29. The inner and outer fins 29,31include brackets 46 that rest on a machined insert 47, which is alsowater cooled, that is fit into the opening 19 of the burner block 14.The eight outer fins 31 are spring loaded to maintain a tightrelationship with the eight inner fins 29. The outer fin control arms 30interact via roller pins 32 with angled slots 33 in a surroundingcontrol ring 34 so that as the control ring 34 is rotated, the outerends of the fin control arms 30 are raised or lowered, thereby pivotingthe eight inner fins 29. In this manner, the collar 28 effectivelyvaries the cross-sectional area of the annular channel 27 between thesleeve 17 and the collar 28.

As best seen in FIG. 9, the control ring 34 is held in place by aplurality of rollers 35 positioned on a circular support frame 36 suchthat the rollers 35 bear on the outer face and the upper and lower edgesof the control ring 34. The rollers are journalled in pivot mounts 37 toadjust their position. The control ring 34 can be rotated by means of aworm gear 38 and motor 39. Alternatively, the control ring could berotated by means of a pivot arm assembly or chain and sprocket driveusing either hydraulic, pneumatic or electrical actuators.

As seen in FIGS. 5 and 6, the collar 28 includes an upper section 40having a flange 41 that connects with a corresponding lower flange 42 atthe lower rim 43 of the wind box 15. The upper section 40 of the collar28 connects to the inner and outer fins 29, 31 by means of cooperatinglugs 44. A steel tension hoop 45 covers the gap between the upper ringand the fins.

Cover plates 48 are mounted to the control ring support frame 36 toenclose the area. A compressed air inlet is provided to maintain apositive pressure within the enclosure formed by the cover plates toprevent either combustion air or furnace gases from escaping.

As shown in FIGS. 3 and 4, and 10-13, the upper end of the injectorsleeve 17 has flanges 50,51 for mounting the injector 16 tocorresponding flanges 52,53 on the wind box 15 and the distributor 23.The upper flange 52 of the wind box 15 and the lower flange 50 of thesleeve 17 are separated by a compression gasket 54 and provided withthree-point leveling adjusters 55. This allows the injector 16 to becorrectly centered to provide equalized air flow through the annularchannel 27 between the sleeve 17 and the collar 28. The adjusters 55consist of three studs welded to the wind box upper flange 52, providedwith wing nuts to allow easy adjustment without requiring additionaltools.

In addition, as shown in FIGS. 5 and 6, rodding mechanisms 57 areprovided at three points on the lower portion of the wind box 14 to givefeedback of the alignment of the injector sleeve 17 relative to thecollar 28. The sleeve 17 is set during cold installation and the roddingmechanisms 57 are each calibrated to the stroke distance to touch thesleeve 17. The zero point can be checked periodically during furnacecampaigns and deviations can be corrected by means of the levelingadjusters 55.

The wind box 15 is a generally biconical barrel shape and provided withinspection ports 58 where the burner flame can be observed, and alsowhere the verticality of the injector 16 can be visually assessed. Thewind box 15 is provided with four beams 59 by which the burner assembly13 is mounted to the support frame of the furnace. Two or moresymmetrically arranged inlets may be used to promote symmetric flow ofthe combustion gas through the nozzle opening 19. The wind box 15 isdimensioned to provide sufficient volume to substantially slow down theincoming combustion gas so that the pressure distribution of thecombustion gas is made effectively uniform. A reduction in velocity ofbetween 20% and 90% of the inlet velocity has been found advantageous.This promotes a more even flow through the nozzle. It also buffers outvariations in flow rates from multiple inlets. The interior of the windbox 15 is smooth and the lower surface of the wind box 15 merges via asmooth transition to the nozzle opening 19 to promote streamline flow.

Turning to FIGS. 10-13, the central lance 18 of the injector 16 and thesleeve 17 both include internal water cooling. (The interior of thesleeve 17 is not shown but it includes either a water cooling coil or ashell design whereby the water flows down the inside of the shell and upthe outside or vice versa.) Cast in place monel tubing 68 providescooling for the lance tip 25. The lance 18 has small guide wings 60 tokeep it centered within the sleeve 17 and is mounted with spring washers61 to maintain tension. An auxiliary fuel line 62 extends through thelance 18 to a central outlet 63 at the bottom of the tip 25. Coolinglines 64 for the lance 18 are clustered around the auxiliary fuel line62. The compressed air carried through the lance 18 is dischargedthrough an annular discharge slot 65 that extends around the tip 25 toform an effective continuous air curtain. Gussets 66 and a base ring 67maintain the gap at a constant cross-section so that the flow is notchoked prior to going through the slot 65. The dimension of the gapprovided by the slot 65 can be adjusted by replacing the base ring 67with a thicker or thinner base ring, or by adding shims.

Above the burner assembly 13 is the feed equipment. As seen in FIGS.14-18, pulverous feed material such as copper sulfide concentrates ischarged via air slides 20. Two air slides 20 are provided forredundancy. The feed material passes from each air slide 20 through asplitter box 21 that separates the charge into four equal portions. Theoutlet of each splitter box 21 passes through a manifold connector 12where feed pipes 22 are attached. Pairs of feed pipes 22 from eachsplitter box 20 and manifold connector 12 are combined to provide fourcharging streams to the feed distributor 23. Each stream of feedmaterial goes into one quadrant of the distributor 23. In each quadrant,the feed stream is distributed evenly by means of a curved plate 11 thatdirects the feed material evenly around the quadrant of the feeddistributor. The feed material then flows in an evenly distributedannulus into the sleeve 17 of the burner injector 16.

Turning to FIGS. 19-21, an alternate embodiment is shown. Similarcomponents are given like names, and like reference numbers followed bythe letter “a”, and their description will not be repeated.

In this embodiment, the injector sleeve 17 a is supported by threemechanical screw actuators 71. The actuators 71 serve to adjust theheight of the sleeve 17 a as well as to center the injector 16 a. Theyallow for precise raising and lowering of the sleeve 17 a when they aremoved in unison, and they allow for centering of the injector 16 a whenthey are controlled separately. The centering can be automated by havingthree feedback sensors that provide feedback of the relative height ofeach of the actuators 71 to the controller. The sensors may be yo-yotype sensors or other sensors such as optical sensors.

The wall of the lower portion of the injector sleeve 17 a is enlarged topresent an upward taper to its outer surface, while the inner surface ofthe insert 47 a is tapered downwardly at a similar but shallower angle.The annular channel 27 a between the injector sleeve 17 a and the blockinsert 47 a is in its most open position when the actuators 71 are fullyextended. At this point, the sleeve 17 a is at its highest position andthe cross-sectional area through which the combustion air enters thereaction shaft is at its maximum. As the actuators 71 are lowered, thesleeve 17 a is also lowered, which gradually closes off thecross-sectional area where the combustion air enters the reaction shaft.When the actuators 71 are retracted, the sleeve 17 a is at its lowestposition and the annular area through which the enriched air enters thereaction shaft is at its minimum. In this way the cross-sectional areaof the annular channel 27 a can be adjusted, which in turn adjusts thevelocity of the combustion air enters the reaction shaft.

As the injector sleeve 17 a moves, the injector 16 a and the distributor23 a move as well. The feed pipes 22 a, however, do not move. The linearmotion is accommodated through the use of four expansion joints 72attached to the inlets of the charge distributor 23 a and the outlets ofthe feed pipes 22 a.

Turning to FIGS. 22-24, a third embodiment is shown. Similar componentsare given like names, and like reference numbers followed by the letter“b”, and their description will not be repeated.

In this embodiment, the lower portion of the sleeve 17 b has a bellshape with a downwardly flared section 81 terminating in a generallystraight lower rim section 82. A generally straight and cylindricalouter collar 80 extends from the block 14 b to the wind box 15 b. Withinthe outer collar 80 are mounted a plurality of sliding bands 83. Thesliding bands are raised and lowered by actuators (not shown) that areexterior to the insert 47 b and exterior to the wind box 15.

The annular channel 27 b between the injector sleeve 17 b and the blockinsert 47 b is in its most open position when the sliding bands arefully raised. At this point, the cross-sectional area through which thecombustion air enters the reaction shaft is at its maximum. As thesliding bands are lowered, the cross-sectional area where the combustionair enters the reaction shaft is reduced. When the sliding bands are attheir lowest position the annular area through which the enriched airenters the reaction shaft is at its minimum. In this way thecross-sectional area of the annular channel 27 b can be adjusted, whichin turn adjusts the velocity of the combustion air enters the reactionshaft.

Turning to FIGS. 25-29 c, a further embodiment is shown. Similarcomponents are given like names, and like reference numbers followed bythe letter “c”, and their description will not be repeated.

In this embodiment, the burner block 84 is a fabricated steel andstainless steel double walled construction with water cooling. The windbox 15 c connects to the block 84 with a tapered connection 87 thatsurrounds the lower portion of the injector 16 c

The distributor 23 c mounts lower, partially within the wind box 15 c,to reduce the overall height of the burner. The distributor 23 c has noquadrant partitions and instead of curved plates, the feed material isdeflected evenly around the injector sleeve 17 c with a frustoconicalskirt 86. The wind box 15 c connects with the block 84 through thetapered connection 87. The injector sleeve 17 c is enlarged at its lowerportion to present an upward taper to its outer surface. The innersurface of the connection 87 is similarly tapered but at a shallowerangle. The annular channel 27 c between the injector sleeve 17 c and theconnection 87 is adjusted by raising and lowering the injector sleeve 17c by means of actuators 71 c. Fins 85 within the connection 87 help tomaintain the concentricity and verticality of the injector 16 c. Thefins 85 also aid in reducing turbulence of the airflow. The connection87 may be made of a ceramic material, or may be coated with ceramic orother refractory to protect it from the heat of the reaction shaft.

Turning to FIGS. 29 a, 29 b and 29 c, each of the inspection ports 58 cincludes a cylindrical casing 90 having a hinged cover 91 that holds thesight glass 92. The hinged cover can be locked in place by means of alatch 93, or can be opened, for example, to allow operators to takemeasurements. The latch 91 includes a screw mechanism which can be usedto ensure that the cover is closed tightly, so as to compress a gasketbetween it and the casing 90 to create a seal. An interior guard 94protects the inside of the sight glass 92. The guard 94 can pivot bymeans of a handle 95. The handle 95 is heavier than the guard 94 and isoriented so that the force of gravity acting on the handle 95 will biasthe guard 94 to its closed position. When an operator wishes to viewinside the burner, the operator pulls up on the handle 95 which rotatesthe guard 94 downwardly and out of the way.

It will be appreciated by those skilled in the art that many variationsare possible within the scope of the claimed subject matter. Theembodiments that have been described above are intended to beillustrative and not defining or limiting. For example, the collar ofthe third embodiment could be a single piece that can be moved up anddown to increase or decrease the cross-sectional area of the annularchannel and thereby control the velocity of the combustion air enteringthe reaction shaft. In addition, the tip of the lance could be providedwith additional compressed air ports to aid in fluidizing the descendingfeed material above the air curtain.

1. A burner for a flash smelting furnace, comprising: a burner blockthat integrates with the roof of the furnace, the block having a nozzleopening therethrough to communicate with the reaction shaft of thefurnace; a wind box to supply combustion gas to the reaction shaftthrough the nozzle opening, the wind box being mounted over the nozzle;an injector having a sleeve for delivering pulverous feed material tothe furnace and having a central lance within the sleeve to supplycompressed air for dispersing the pulverous feed material in thereaction shaft, the injector mounting within the wind box so as toextend through the nozzle opening in the block, defining therewith anannular channel through which combustion gas from the wind box issupplied into the reaction shaft; and a distributor for receivingpulverous feed material from a plurality of feed pipes, the distributorhaving at least one curved deflector that directs the feed stream in anevenly distributed annulus into the burner sleeve.
 2. The burner ofclaim 1 wherein the at least one curved deflector comprises a pluralityof deflector plates arranged in quadrants of the distributor.
 3. Theburner of claim 1 wherein the at least one curved deflector comprises afrustoconical skirt.
 4. The burner of claim 1 wherein the distributormounts at least partially within the upper portion of the wind box. 5.The burner of claim 1 further comprising at least one inspection portmounted to the wind box, the inspection port comprising a sight glasswith an internal guard movable from a first position protecting thesight glass to a second position allowing viewing through the sightglass.
 6. The burner of claim 5 wherein the internal guard is movable bymeans of an external handle.
 7. The burner of claim 6 wherein theinternal guard is biased to rest normally in the first position.
 8. Theburner of claim 1, wherein the wind box is dimensioned to havesufficient volume to substantially slow down the incoming combustion gasso that the pressure distribution is made effectively even.
 9. Theburner of claim 8, wherein the wind box is dimensioned to achieve areduction in velocity of the combustion gas of between 20% and 90% ofthe inlet velocity.
 10. The burner of claim 8, wherein the wind box hasa generally biconical shape.
 11. The burner of claim 8, wherein the windbox has at least two combustion gas inlets arranged radiallysymmetrically.
 12. The wind box of claim 11 comprising two opposedcombustion gas inlets.
 13. The burner of claim 8, wherein the interiorsurface of the lower portion of the wind box mergers with the nozzleopening so as to provide a smooth transition.